You could just try using AQ salt for mild fin rot, 1 tsp per gallon :)

You can never ask too many questions in my opinion, the more you ask about, the more you'll know, and the less you'll have to struggle figuring out on your own ^^
Most of us (if not ALL of us) each love our fishes, you're not alone :)

I agree, start with conservative treatment. Put him in a heated 1 gallon container and add 1tsp. aquarium salt per gallon, with daily 100% water changes to keep the level of salt consistent. Make sure the salt is fully dissolved before you add it. Treat for up to 10 days and let us know if he's improved.